Black people in the United States have a much higher prevalence of essential hypertension than whites. Causes of this difference are speculative but, differences in diet, renal physiology and socioecologic factors have been implicated. A high level of autonomic nervous system (ANS) reactivity to emotionally challenging stimuli has also been related to the development of essential hypertension. The presently proposed project will focus upon the propostion that black-white differences in renal function, an elevated intake of sodium, a high level of psychosocial and socioecologic stress, and a high level of ANS reactivity to emotionally stressful situations interact to produce the very high, disproportionate prevalence of borderline hypertension that has been reported for poor inner-city blacks. In order to study this proposition the proposed project would examine in 320 25-44 year old Miami residents, cardiovascular (i.e., heart rate, blood pressure, rate-pressure product) and hormonal (i.e., plasma epinephrine, norepinephrine, renin, cortisol) responses to standardized, laboratory, biobehavioral challenges (i.e., bicycle ergometer, competitive video game, cold pressor test, Type A structured interview). Cardiovascular and hormonal responses to the biobehavioral challenges will be specifically compared as a function of race, sex, socioeconomic status and normal blood pressure versus borderline hypertension. The results will be further analyzed as a function of dietary (e.g., sodium, potassium, and calcium intake), genetic, (i.e., family history of hypertension), organismic (i.e., urinary sodium, potassium, calcium; plasma renin, cortisol, catecholamines, aerobic fitness; obesity), and psychological (e.g., alienation; anger expression; chronic anxiety) variables. Extent to which the reactivity findings obtained in the laboratory generalize to everyday life will be examined using ambulatory electrocardiographic and blood pressure monitoring.